The problem of estimating or measuring the change in shape, or deformation, of a manufactured product is one of a general character. There is today a general need to estimate or measure the change in shape or deformation of a product under manufacture, so that when carrying out prototype checks it is possible to anticipate what constructional changes, e.g. tool changes, will be needed and so that when carrying out production checks (quality checks) the need for taking rectifying measures, e.g. tool replacement because of worn tools, can be both observed and put into effect at an early stage, thereby greatly reducing the number of faulty goods which need to be rejected, if not avoiding the occurrence of rejects altogether, particularly when the product is manufactured in large numbers.
The problem of measuring or estimating the deformation or change in shape of a product is particularly prevalent in products produced from polymeric materials, due to the anisothropic properties of the injection moulded products; even though measurements are taken at given points, no definite knowledge can be obtained of the circumstances prevailing at the points therebetween. In addition, because the material is resilient it can readily be deformed or blemished by contact with gauges, templates, measuring probes etc., when the product is measured for distortion by means of a conventional contact method. Certain products are used normally in a humid atmosphere, and hence the lack of a practical method of measuring moist products is a distinct disadvantage.